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Title
Collaboration based spectrum sharing algorithms in cognitive radio networks
Creator
Hyder, Chowdhury Sayeed
Date
2017
Collection
Electronic Theses & Dissertations
Description
"Radio spectrum assignment to wireless providers using traditional fixed allocation policy will no longer be a viable technique to meet the growing spectrum demand of emerging wireless applications. This is because while the available pool of unassigned radio spectrum is low, the spectrum already assigned to existing applications is also often underutilized in time, frequency, and location. With features like transmission flexibility and adaptability cognitive radio (CR) provides a useful...
Show more"Radio spectrum assignment to wireless providers using traditional fixed allocation policy will no longer be a viable technique to meet the growing spectrum demand of emerging wireless applications. This is because while the available pool of unassigned radio spectrum is low, the spectrum already assigned to existing applications is also often underutilized in time, frequency, and location. With features like transmission flexibility and adaptability cognitive radio (CR) provides a useful means of spectrum sharing among growing users as an alternative to the current fixed policy. The cognitive radio network (CRN), based on the functionality of CR, consists of two types of users -- primary users (PU) and secondary users (SU). Primary users are licensed users who have exclusive access rights of a fixed spectrum range. Secondary users are unlicensed users who opportunistically exploit the spectrum holes or negotiate with primary users to earn transmission access rights. The CRN based efficient spectrum sharing algorithms work on different forms of collaboration between the PUs and the SUs (inter-user collaboration) and among the SUs themselves (intra-user collaboration). In the sensing based collaboration model, the SUs sense licensed spectrum and collaboratively decide about its availability based on the sensing results without any involvements from the PUs. In the relay based collaboration model, the SUs coordinate with the PUs directly, relay primary packets in exchange for transmission opportunities, and thus build a win-win cooperative framework to attain mutual benefits. In the auction based collaboration model, the SUs bid for temporary or permanent usage rights of unused licensed spectrum bands that are put into auction for sale by the PUs. Each of these collaboration models faces different sets of challenges towards achieving high spectrum utilization. In this dissertation, we address some of these challenges and present a set of efficient spectrum sharing algorithms based on these collaboration models. The first work in this dissertation addresses the spectrum sensing data falsification (SSDF) attack in IEEE 802.22 wireless regional area network (WRAN) under the sensing based collaboration model. We discuss different strategies of manipulating sensing reports by one or more malicious users and how these manipulation strategies may affect the spectrum utilization. To defend against such malicious attacks, we present an adaptive reputation based clustering algorithm. The algorithm combines the clustering technique with feedback based reputation adjustment to prevent independent and collaborative SSDF attacks and quarantines the attackers from the decision making process. Our next set of work in this dissertation falls under the relay based collaboration model. We investigate the feasibility of this collaboration model in the case of real-time applications. We quantify the impact of packet deadlines and cooperation overhead on the system performance. We discuss the impact of interference that may cause from secondary transmissions. Based on the analysis, we develop an interference aware reliable cooperative framework which improves the packet reception rate of both users with low overhead. We extend our investigation of this relay based collaboration model from single hop to multiple hops in the form of cooperative routing. We formulate the routing problem as an overlapping coalition formation game where each coalition represents a routing path between primary source and destination consisting of multiple SUs as intermediate relays. The proposed model allows SUs to participate in more than one coalitions and creates more transmission opportunities for them while achieving stable routing paths for PUs. Our final set of work in this dissertation deals with the challenges in the auction based collaboration model. We consider an online setting of spectrum auctions where participation and valuation of both bidders and sellers are stochastic. We analyze the behavior of bidders and sellers in such settings and develop truthful auction mechanisms with respect to bid and time, improving spectrum reuse, auction efficiency, and revenue. The findings from our research will help to understand the underlying challenges in future networks, build a better spectrum ecosystem, and encourage new spectrum sharing models in wireless broadband communications."--Pages ii-iv.
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Title
Secure and efficient spectrum sharing and QoS analysis in OFDM-based heterogeneous wireless networks
Creator
Alahmadi, Ahmed S.
Date
2016
Collection
Electronic Theses & Dissertations
Description
"The Internet of Things (IoT), which networks versatile devices for information exchange, remote sensing, monitoring and control, is finding promising applications in nearly every field. However, due to its high density and enormous spectrum requirement, the practical development of IoT technology seems to be not available until the release of the large millimeter wave (mmWave) band (30GHz-300GHz). Compared to existing lower band systems (such as 3G, 4G), mmWave band signals generally require...
Show more"The Internet of Things (IoT), which networks versatile devices for information exchange, remote sensing, monitoring and control, is finding promising applications in nearly every field. However, due to its high density and enormous spectrum requirement, the practical development of IoT technology seems to be not available until the release of the large millimeter wave (mmWave) band (30GHz-300GHz). Compared to existing lower band systems (such as 3G, 4G), mmWave band signals generally require line of sight (LOS) path and suffer from severe fading effects, leading to much smaller coverage area. For network design and management, this implies that: (i) MmWave band alone could not support the IoT networks, but has to be integrated with the existing lower band systems through secure and effective spectrum sharing, especially in the lower frequency bands; and (ii) The IoT networks will have very high density node distribution, which is a significant challenge in network design, especially with the scarce energy budget of IoT applications. Motivated by these observations, in this dissertation, we consider three problems: (1) How to achieve secure and effective spectrum sharing? (2) How to accommodate the energy limited IoT devices? (3) How to evaluate the Quality of Service (QoS) in the high density IoT networks? We aim to develop innovative techniques for the design, evaluation and management of future IoT networks under both benign and hostile environments. The main contributions of this dissertation are outlined as follows. First, we develop a secure and efficient spectrum sharing scheme in single-carrier wireless networks. Cognitive radio (CR) is a key enabling technology for spectrum sharing, where the unoccupied spectrum is identified for secondary users (SUs), without interfering with the primary user (PU). A serious security threat to the CR networks is referred to as primary user emulation attack (PUEA), in which a malicious user (MU) emulates the signal characteristics of the PU, thereby causing the SUs to erroneously identify the attacker as the PU. Here, we consider full-band PUEA detection and propose a reliable AES-assisted DTV scheme, where an AES-encrypted reference signal is generated at the DTV transmitter and used as the sync bits of the DTV data frames. For PU detection, we investigate the cross-correlation between the received sequence and reference sequence. The MU detection can be performed by investigating the auto-correlation of the received sequence. We further develop a secure and efficient spectrum sharing scheme in multi-carrier wireless networks. We consider sub-band malicious user detection and propose a secure AES-based DTV scheme, where the existing reference sequence used to generate the pilot symbols in the DVB-T2 frames is encrypted using the AES algorithm. The resulted sequence is exploited for accurate detection of the authorized PU and the MU. Second, we develop an energy efficient transmission scheme in CR networks using energy harvesting. We propose a transmitting scheme for the SUs such that each SU can perform information reception and energy harvesting simultaneously. We perform sum-rate optimization for the SUs under PUEA. It is observed that the sum-rate of the SU network can be improved significantly with the energy harvesting technique. Potentially, the proposed scheme can be applied directly to the energy-constrained IoT networks. Finally, we investigate QoS performance analysis methodologies, which can provide insightful feedbacks to IoT network design and planning. Taking the spatial randomness of the IoT network into consideration, we investigate coverage probability (CP) and blocking probability (BP) in relay-assisted OFDMA networks using stochastic geometry. More specifically, we model the inter-cell interference from the neighboring cells at each typical node, and derive the CP in the downlink transmissions. Based on their data rate requirements, we classify the incoming users into different classes, and calculate the BP using the multi-dimensional loss model."--Pages ii-iii.
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Title
Holistic performance control for mission-critical cyber-physical systems
Creator
Chen, Jinzhu
Date
2014
Collection
Electronic Theses & Dissertations
Description
Recent years have seen the growing deployments of Cyber-Physical Systems (CPSs) in many mission-critical applications such as security, civil infrastructure, and transportation. These applications often impose stringent performance requirements on system sensing fidelity, timeliness, energy efficiency and reliability. However, existing approaches treat these concerns in isolation and hence are not suitable for CPSs where the...
Show moreRecent years have seen the growing deployments of Cyber-Physical Systems (CPSs) in many mission-critical applications such as security, civil infrastructure, and transportation. These applications often impose stringent performance requirements on system sensing fidelity, timeliness, energy efficiency and reliability. However, existing approaches treat these concerns in isolation and hence are not suitable for CPSs where the system performances are dependent of each other because of the tight integration of computational and physical processes. In this dissertation, we investigate the dependencies between these performances and propose the holistic performance control approaches for two typical mission-critical CPSs, which are Wireless Cyber-phyiscal Surveillance (WCS) systems and data centers. We first propose a holistic approach called {\em Fidelity-Aware Utilization Controller} (FAUC) for WCS systems that combine low-end sensors with cameras for large-scale ad hoc surveillance in unplanned environments. By integrating data fusion with feedback control, FAUC enforces a CPU utilization upper bound to ensure the system's real-time schedulability under dynamic CPU workloads at runtime because of stochastic detection results. At the same time, FAUC optimizes system fidelity and adjusts the control objective of CPU utilization adaptively in the presence of variations of target/noise characteristics. The testbed experiments and the trace-driven simulations show that FAUC can achieve robust fidelity and real-time guarantees in dynamic environments.We then present a proactive thermal and energy control approach for data centers to improve the energy efficiency while ensuring the data center reliability. It consists of a high-fidelity real-time temperature prediction system and a predictive thermal and energy control (PTEC) system. The prediction system integrates Computational Fluid Dynamics (CFD) modeling, in situ wireless sensing and real-time data-driven prediction. To ensure the forecasting fidelity, we leverage the realistic physical thermodynamic models of CFD to generate transient temperature distribution and calibrate it using sensor feedback. Both simulated temperature distribution and sensor measurements are then used to train a real-time prediction algorithm. Based on the temperature prediction system, we propose the PTEC system, which leverages the server built-in sensors and monitoring utilities, as well as a network of wireless sensors to monitor the thermal and power conditions of a data center. It predicts the server inlet temperatures in real-time, and optimizes temperature setpoints and cold air supply rates of cooling systems, as well as the speeds of server internal fans, to minimize their overall energy consumption. To ensure the data center reliability, PTEC enforces a set of thermal safety requirements including the upper bounds on server inlet temperatures and their variations, to prevent server overheating and reduce server hardware failure rate. A partition-based approach is proposed to solve the control problem efficiently for large-scale data centers. Extensive testbed experiments and trace-driven CFD simulations show that PTEC can safely reduce substantial cooling and circulation energy consumption compared with traditional approaches, and can adapt to the realistic and dynamic data center workload.
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Title
Toward efficient spectrum use in multicarrier wireless networks
Creator
Huang, Pei
Date
2014
Collection
Electronic Theses & Dissertations
Description
The last decade has witnessed growing interest in dynamic spectrum access, which is motivated by the observation that a large portion of the radio spectrum has been licensed but remains highly underutilized while a few small unlicensed bands that are open to anyone are getting more crowded due to the explosive expansion of wireless services. To provide more flexible access to radio spectrum, dynamic spectrum access is introduced to enable unlicensed users to opportunistically utilize vacant...
Show moreThe last decade has witnessed growing interest in dynamic spectrum access, which is motivated by the observation that a large portion of the radio spectrum has been licensed but remains highly underutilized while a few small unlicensed bands that are open to anyone are getting more crowded due to the explosive expansion of wireless services. To provide more flexible access to radio spectrum, dynamic spectrum access is introduced to enable unlicensed users to opportunistically utilize vacant spectrum chunks (known as spectrum holes) in licensed frequency bands.In dynamic spectrum access, non-contiguous orthogonal frequency division multiplexing (NC-OFDM) is widely adopted to efficiently utilize fragmented spectrum because it is convenient to keep silent on some spectrum fragments to avoid interference with licensed users. In NC-OFDM, a band of spectrum is divided into many orthogonal subcarriers and data are transmitted on a subset of them simultaneously. The subcarriers that interfere with the licensed users are deactivated. Because each subcarrier can be managed independently, this dissertation introduces a series of techniques that exploit the subcarriers to address problems in dynamic spectrum access.When unlicensed users called secondary users (SUs) are granted the permission to operate in the licensed bands, they must ensure that the interference caused by them to licensed users known as primary users (PUs) is within a limit. Even without such a requirement, SUs should avoid as many collisions as possible. To improve spectrum hole extraction rate and reduce collision rate, we propose a spectrum occupancy prediction model that helps estimate the spectrum availability. It measures a wide band of spectrum with OFDM and groups subcarriers to subchannels based on spectrum use activities. In each subchannel, frequent spectrum occupancy patterns are identified and used to predict future channel states (i.e., busy or idle). With the prediction, SUs are able to make use of spectrum holes more aggressively without introducing undue interference to PUs.In the spectrum holes discovered above, a mechanism is needed to coordinate medium access between devices. Because devices opportunistically utilize spectrum holes, a device may experience severe contentions with devices from various applications. We propose a collision detection and bitwise arbitration (CDBA) mechanism that quickly identifies the winner in a contention using combined information from both the time domain and the frequency domain. It enables collision detection in the frequency domain by selectively deactivating subcarriers at each transmitter.The CDBA assumes that all devices adopt the same channel width, but different radio technologies have different requirements on channel width. When heterogeneous radios coexist in a contention domain, wideband devices can hardly win medium access opportunities in contention with narrowband devices. To address the problem, we propose an adaptive channel bonding protocol in which a wideband device initiates transmission as long as there exist some idle narrow channels and gradually increases channel width during transmission whenever new narrow channels become available. To increase the chance to win some narrow channels, a wideband device contends on subcarriers of each narrow channel with a different priority.After the contention problem is addressed, we study how to increase the transmission speed when a device is granted the permission to transmit. As wireless networks move toward wider channel widths, it is common that different subcarriers experience different fade. To cope with the frequency-selective fading, modulation scheme for each subcarrier should be selected based on the subcarrier channel quality. We exploit the modulation diversity in our modulation scheme coding to improve network throughput.Besides unicast, broadcast is another fundamental mechanism in wireless networks. Because devices utilize spectrum fragments opportunistically, different receivers may have different vacant spectrum fragments at different locations. The broadcast is more challenging in dynamic spectrum access because the transmitter needs to consider the diversity of spectrum availability. We propose a spectrum fragment agile broadcast (SFAB) protocol to support broadcast under nonuniform spectrum availability. It encodes unique sequences on subcarriers of each spectrum fragment to achieve fast spectrum agreement between the transmitter and the receivers.
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Title
Defense against primary user emulation attacks in cognitive radio networks using advanced encryption standard
Creator
Alahmadi, Ahmed Salah
Date
2014
Collection
Electronic Theses & Dissertations
Description
This thesis considers primary user emulation attacks (PUEA) in cognitive radio networks operating in the white spaces of the digital TV (DTV) band. We propose a reliable AES-assisted DTV scheme, in which an AES-encrypted reference signal is generated at the TV transmitter and used as the sync bits of the DTV data frames. By allowing a shared secret between the transmitter and the receiver, the reference signal can be regenerated at the receiver and used to achieve accurate identification of...
Show moreThis thesis considers primary user emulation attacks (PUEA) in cognitive radio networks operating in the white spaces of the digital TV (DTV) band. We propose a reliable AES-assisted DTV scheme, in which an AES-encrypted reference signal is generated at the TV transmitter and used as the sync bits of the DTV data frames. By allowing a shared secret between the transmitter and the receiver, the reference signal can be regenerated at the receiver and used to achieve accurate identification of the authorized primary users. Moreover, when combined with the analysis on the auto-correlation of the received signal, the presence of the malicious user can be detected accurately no matter the primary user is present or not. We analyze the effectiveness of the proposed approach through both theoretical analysis and simulation examples. It is shown that with the AES-assisted DTV scheme, the primary user, as well as malicious user, can be detected with high accuracy under primary user emulation attacks. It should be emphasized that the proposed scheme requires no changes in hardware or system structure except of a plug-in AES chip. Potentially, it can be applied directly to today's DTV system under primary user emulation attacks for more efficient spectrum sharing.
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Title
Stochastic modeling of routing protocols for cognitive radio networks
Creator
Soltani, Soroor
Date
2013
Collection
Electronic Theses & Dissertations
Description
Cognitive radios are expected torevolutionize wireless networking because of their ability tosense, manage and share the mobile available spectrum.Efficient utilization of the available spectrum could be significantly improved by incorporating different cognitive radio based networks. Challenges are involved in utilizing the cognitive radios in a network, most of which rise from the dynamic nature of available spectrum that is not present in traditional wireless networks. The set of available...
Show moreCognitive radios are expected torevolutionize wireless networking because of their ability tosense, manage and share the mobile available spectrum.Efficient utilization of the available spectrum could be significantly improved by incorporating different cognitive radio based networks. Challenges are involved in utilizing the cognitive radios in a network, most of which rise from the dynamic nature of available spectrum that is not present in traditional wireless networks. The set of available spectrum blocks(channels) changes randomly with the arrival and departure of the users licensed to a specific spectrum band. These users are known as primary users. If a band is used by aprimary user, the cognitive radio alters its transmission power level ormodulation scheme to change its transmission range and switches to another channel.In traditional wireless networks, a link is stable if it is less prone to interference. In cognitive radio networks, however, a link that is interference free might break due to the arrival of its primary user. Therefore, links' stability forms a stochastic process with OFF and ON states; ON, if the primary user is absent. Evidently, traditional network protocols fail in this environment. New sets of protocols are needed in each layer to cope with the stochastic dynamics of cognitive radio networks.In this dissertation we present a comprehensive stochastic framework and a decision theory based model for the problem of routing packets from a source to a destination in a cognitive radio network. We begin by introducing two probability distributions called ArgMax and ArgMin for probabilistic channel selection mechanisms, routing, and MAC protocols. The ArgMax probability distribution locates the most stable link from a set of available links. Conversely, ArgMin identifies the least stable link. ArgMax and ArgMin together provide valuable information on the diversity of the stability of available links in a spectrum band. Next, considering the stochastic arrival of primary users, we model the transition of packets from one hop to the other by a Semi-Markov process and develop a Primary Spread Aware Routing Protocol (PSARP) that learns the dynamics of the environment and adapts its routing decision accordingly. Further, we use a decision theory framework. A utility function is designed to capture the effect of spectrum measurement, fluctuation of bandwidth availability and path quality. A node cognitively decides its best candidate among its neighbors by utilizing a decision tree. Each branch of the tree is quantified by the utility function and a posterior probability distribution, constructed using ArgMax probability distribution, which predicts the suitability of available neighbors. In DTCR (Decision Tree Cognitive Routing), nodes learn their operational environment and adapt their decision making accordingly. We extend the Decision tree modeling to translate video routing in a dynamic cognitive radio network into a decision theory problem. Then terminal analysis backward induction is used to produce our routing scheme that improves the peak signal-to-noise ratio of the received video.We show through this dissertation that by acknowledging the stochastic property of the cognitive radio networks' environment and constructing strategies using the statistical and mathematical tools that deal with such uncertainties, the utilization of these networks will greatly improve.
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Title
A localized and distributed channel assignment framework for cognitive radio networks
Creator
Plummer, Anthony Tyrone
Date
2007
Collection
Electronic Theses & Dissertations